I use Sandboxie for 2 purposes :
- Testing some softwares promptly
- Working on some projects limited in time

For this 2nd usage, it would be cool to be able to test a software, or a different configuration in a lower-level sandbox without modifying the 1st one. For now, I do a copy of the sandbox folder before making my changes, and then I revert to this copy when I'm finished with my tests.

And the top would be to be able to merge or not the 2 sandboxies at the end of the tests.

That sounds like merging snapshots or 2 instances of virtual environements on the fly. I believe that was mentioned as a commonly requested feature that won't be implemented. Check the sticky in this subforum.

My feature request was principally about the nested sandboxes. The merging feature would be an extension of this. But you're right : this part is very close from what had been discussed in the Common Features Requests and had been rejected. So I remove this part of the proposal.